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Update docs on workaround for modern MSVC/C++ in Python 2.7

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Yannick Jadoul
2020-05-04 23:39:59 +02:00
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@@ -30,6 +30,14 @@ For more details see https://en.cppreference.com/w/cpp/compiler_support, https:/
## Windows and Python 2.7
Visual C++ for Python 2.7 does not support modern standards of C++. When building on Appveyor, you will need to either use the "Visual Studio 2017" or "Visual Studio 2019" image, but Python 2.7 is not supported on these images - skip it by setting `CIBW_SKIP=cp27-win*`.
Visual C++ for Python 2.7 does not support modern C++ standards (i.e., C++11 and later). When building on Appveyor, you will need to either use the "Visual Studio 2017" or "Visual Studio 2019" image, but Python 2.7 is not supported on these images - skip it by setting `CIBW_SKIP=cp27-win*`.
There is an optional workaround for this, though: the pybind11 project argues and shows that it is [possible to compile Python 2.7 extension with a newer compiler](https://pybind11.readthedocs.io/en/stable/faq.html#working-with-ancient-visual-studio-2008-builds-on-windows) and has an example project showing how to do this: https://github.com/pybind/python_example. The main catch is that a user might need to install a newer "Microsoft Visual C++ Redistributable", since the newer C++ standard libraries are not included by default with the Python 2.7 installation.
There is an optional workaround for this, though: the pybind11 project argues and shows that it is [possible to compile Python 2.7 extension with a newer compiler](https://pybind11.readthedocs.io/en/stable/faq.html#working-with-ancient-visual-studio-2008-builds-on-windows) and has an example project showing how to do this: https://github.com/pybind/python_example. The main catch is that a user might need to install [a newer "Microsoft Visual C++ Redistributable"](https://support.microsoft.com/en-us/help/2977003/the-latest-supported-visual-c-downloads), since the newer C++ standard library's binaries are not included by default with the Python 2.7 installation.
Forcing `distutils` or `setuptools` to use a more recent version of MSVC that supports modern C++ can be done in the following way:
1. Set the environment variables `DISTUTILS_USE_SDK=1` and `MSSdk=1`. These two environment variables will tell `distutils`/`setuptools` to not search and set up a build environment that uses Visual C++ for Python 2.7 (aka. MSVC 9).
2. Set up the build Visual Studio build environment you want to use, making sure that e.g. `PATH` contains `cl`, `link`, etc.
- Usually, this can be done through `vcvarsall.bat x86` or `vcvarsall.bat x64`. The exact location of this file depends on the installation, but the default path for VS 2019 Community (e.g. used in AppVeyor's `Visual Studio 2019` image) is `C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat`. **Note**: `vcvarsall.bat` changes the environment variables, so this cannot be run in a subprocess/subshell and consequently running `vsvarsall.bat` in `CIBW_BEFORE_BUILD` does not have any effect.
- In Azure Pipelines, [a `VSBuild` task is available](https://docs.microsoft.com/en-us/azure/devops/pipelines/tasks/build/visual-studio-build) and GitHub Actions has [an action `microsoft/setup-msbuild`](https://github.com/microsoft/setup-msbuild) that help setting up the Visual Studio environment.
3. Next, call `cibuildwheel`. Unfortunately, MSVC has separate toolchains for compiling 32-bit and 64-bit, so you will need to run `cibuildwheel` twice: once with `CIBW_BUILD=*-win32` after setting up the `x86` build environment, and once with `CIBW_BUILD=*-win_amd64` in a `x64` enviroment (see previous step).